In two studies the team used the robot to "constantly harrass" one group of 12 rats, and "intermittently" attack another group but only when they moved.

The team led by Hiroyuki Ishii found that the rat which attacked only intermittently depressed the rats the most, especially if the rat had been constantly harassed in its youth.

The aim is to create models of psychological conditions, so that anti-depressants and other drugs might be more effectively tested.

The next tests will pit the team's model of depression against conventional models, which are made by forcing rats and mice to swim for long periods or otherwise have their sense of smell severed.

As the New Scientist says, the research does have positive and interesting applications for humans - but it's hard not to feel that the only thing more depressing that being constantly harassed by a robotic rat is reading the above news story.